1. Field of the Invention
The present invention relates to a medium discharging apparatus and an image forming apparatus to which the medium apparatus is installed.
2. Description of the Related Art
Existing electrophotographic image forming apparatus include printers, copying machines, facsimile machines, and multifunction peripherals. For example, a printer includes an image forming unit that incorporates an LED head, a photoconductive drum, a developing unit, and a transfer unit. The LED head illuminates the charged surface of the photoconductive drum to form an electrostatic latent image on the charged surface. The developing roller supplies toner to the electrostatic latent image to develop the electrostatic latent image with the toner, thereby forming a toner image. The toner image is then transferred by a transfer roller onto a medium, for example, paper.
The paper is fed from a paper cassette to a registry roller, which in turn corrects skew of the paper before feeding the paper to a transfer point defined between the image forming unit and the transfer roller. After the toner image is transferred onto the paper, the paper advances to a fixing unit where the toner image is fixed under pressure and heat. The paper is then discharged onto a stacker.
Since the paper is heated to fuse the toner thereon, the paper may curl after fixing due to the heat and pressure applied thereto.
If sheets of curled paper are stacked on the stacker, the turned-up trailing end portion may interfere with the leading edge of the following sheet discharged from the fixing unit. The leading end of the following sheet may push the trailing end portion of the preceding sheet, causing the preceding sheet to fall off the stacker.
One way of solving this drawback is to employ a film sheet disposed over the exit of the fixing unit, the sheet of film pushing down the raised trailing end portion of the discharged paper.
When the lower end portion of the film sheet interferes with the trailing end portion of the paper, the film is resiliently deformed so that a force is exerted on the raised trailing end portion of the paper. The force varies depending on the mounting location of the film, the warp of the film and the like. This makes it difficult to exert a proper force on the curled trailing end portion of the paper.
As a result, the force may not be exerted on the paper laterally evenly so that the sheets of paper may be discharged with some skew therein.